The figure, released by the Department of Veterans Affairs in February, is based on the agency's own data and numbers reported by 21 states from 1999 through 2011. Those states represent about 40% of the U.S. population. The other states, including the two largest (California and Texas) and the fifth-largest (Illinois), did not make data available.

Who wasn't counted?

People like Levi Derby, who hanged himself in his grandfather's garage in Illinois on April 5, 2007. He was haunted, says his mother, Judy Caspar, by an Afghan child's death. He had handed the girl a bottle of water, and when she came forward to take it, she stepped on a land mine.

When Derby returned home, he locked himself in a motel room for days. Caspar saw a vacant stare in her son's eyes. A while later, Derby was called up for a tour of Iraq. He didn't want to kill again. He went AWOL and finally agreed to a dishonorable discharge.